Apple TV (2nd Gen) AirPlay + Audio Out Sound Quality

Discussion in 'Apple TV and Home Theater' started by Boopyman, Jun 15, 2012.

  1. Boopyman macrumors newbie

    Oct 6, 2009
    So here's my dilemma. I can do either of the following:

    • Convert my ALAC music to 256 kbps and store all of it on my iPhone, before outputting directly to my headphones.
    • Use my iPhone as a remote for my iMac's iTunes, and direct the sound to my 2nd Generation Apple TV, before outputting the signal through optical to my headphones.

    Now, I have my doubts concerning the quality of the Optical Out of the Apple TV: will I be losing quality if I use it ? Furthermore, will AirPlay degrade the quality of my lossless audio ?

    In any event, my question is the following: is it worth putting the second system highlighted above into effect sound quality wise ? I think AirPlay is a bit-perfect way to stream audio, but I could be wrong, and in that situation, the iPhone might simply be a better solution.

    Thanks in advance !

    EDIT: would I also be losing quality using a converter to change the optical out of the Apple TV into a standard 3.5mm female port for my headphones ?
  2. steve-p macrumors 68000


    Oct 14, 2008
    Newbury, UK
    I'll start with the simplest solution first, the iPhone. You may already know this, but If you check the option in iTunes to convert higher quality music and select 256 kbps, it's easy to automatically sync to your iPhone while keeping your lossless files intact. This is worth doing anyway if you have the space, as you then have your music wherever you go. 256 kbps sounds pretty good through headphones. Although the more you spend on headphones, the more likely you will want lossless because quality headphone listening can be very revealing of compression artefacts.

    Moving on to ATV.

    Airplay itself is a lossless transmission scheme. If you send a lossless file, it is sent as is, and arrives at ATV as lossless. If you send a lower bitrate file, say 256 kbps, it gets unconverted to lossless before transmission. That does not improve the quality magically back to that of a lossless file, it just means that it doesn't get any worse if that makes sense.

    There is a slight caveat that the only sample rate ATV supports nowadays is 48KHz which means your 44.1KHz music is rate converted dynamically when it's output, which will have some effect, although it may be slight. It's still very good with lossless source files.

    There is no specific issue with the output quality of the optical out connection. It's still digital at that point. It's really what you plug into it that dictates what happens next.

    Once you have the ATV playing your music, you need to convert the digital audio to analog for your headphones somehow. There are a range of different DACs which can do that, and they will vary in quality and price so you have to choose something that fits your requirements and budget. Also, the analog signal will need amplification somehow. Normally you would connect the optical out to a DAC and then the DAC to a stereo amplifier, or connect the optical out directly to a receiver which has a digital input. Then you would plug your headphones into the amp or receiver. I'm not completely clear how you are intending to do this part.

    Alternatively, you could just plug your headphones into your television. I'm assuming you are connecting your television via HDMI, and HDMI carries the audio too, and your TV will convert it from digital to analog. That way, you would not need anything else.

    As to how to get the audio to your ATV, you have two opposing methods. You can push it using Airplay, when you do that ATV stops whatever it is doing and plays the music you are sending. Or you can pull it using Home Sharing, which is when you tell ATV about your iTunes library and it can play those files itself. So the methods are:

    1. Push using Airplay from your phone, using the 256 Kbps files
    2. Push using Airplay from your computer with iTunes on it. This would be from your lossless library files, and you could control it using the remote application on iPhone if you wanted to. (As well as controlling ATV, it can control iTunes on your computer).
    3. Use the ATV itself to pull the audio files from your iTunes library. Set up home sharing on your ATV so that it can see the library on your iTunes computer. Then, you can use the ATV's UI to play your library files on ATV. Either using the ATV remote, or the iPhone app.

    There are pros and cons for all of these. In practice I use all three, depending on what I am doing. If I don't have the computer on at all, and just want some background music, I just play 256 Kbps music straight off my iPhone to ATV using Airplay. Quality isn't bad. If I want to listen to music properly (and usually quite loud as ATV is connected to a big ass stereo) then I play the lossless files which are in my iTunes library on my computer. Either in iTunes directly pushing via Airplay, or else using ATV to pull them from the iTunes library with Home Sharing. So there are a lot of ways of achieving the same thing.

    The bottom line is it depends how important the quality is to you as to which is the best way, and how flexible you want to be about playing music. I hope I haven't confused you too much, as it's a bit of a can of worms :)
  3. Boopyman thread starter macrumors newbie

    Oct 6, 2009
    Thanks for the great answer !

    I personally have a decent pair of headphones, Denon D5000s, and whether it's the fact they are good or a cognitive problem, I'm certain I can hear the difference between ALAC and 256kbps. :)

    Thanks for reminding me I would need a DAC and amp if I used the optical out, I had somehow just forgotten about that. I was planning on indeed using the Remote app to direct my iTunes on my iMac to play to the Apple TV, which wouldn't even be plugged into a TV. That being said, I'll have to pace myself and save up for a DAC / Amp combo.

    Thanks again for the help.
  4. steve-p macrumors 68000


    Oct 14, 2008
    Newbury, UK
    I may be wrong but you could have a problem if ATV isn't plugged into a TV. I know this used to be the case, but I thought it had been fixed a while back. The other day though I was listening to music using Airplay and I turned the TV off, and the sound stopped working about 30 seconds later. Maybe if it's not connected to start with, it will be OK. Perhaps someone else can chime in with their experiences either way.
  5. Boopyman thread starter macrumors newbie

    Oct 6, 2009
    Thanks for the heads-up, if I ever put the system into place, I'll be sure to comment on this issue !
  6. germanjulian macrumors regular

    Jun 10, 2009
    seems to be fixed
  7. steve-p macrumors 68000


    Oct 14, 2008
    Newbury, UK
    Yes I retested this the other day. If you Airplay to ATV from Mac/iPhone/iPad then it's happy to send audio to an HDMI connected receiver, even if the TV is off. It doesn't seem to care that there's no screen.

    What you can't do is use the ATV UI to start playing music via Home Sharing and then switch the TV off. If you do that, it stops after a few seconds. Which makes sense I guess. It's the same with homesharing video or using NetFlix - if you turn the TV off it pauses ATV after a few seconds.
  8. bizint macrumors newbie

    Dec 8, 2011
    Audio Out Sound Apple TV Streaming Airplay

    I have a similar question which is a helpful addition to this thread (I hope!):

    I have my Apple TV hooked up to my very good assumption is the optical out (and into the amplifier) is lossless...all good.

    Now getting music to play through apple tv... I bought an android phone (cant install itunes)...and also tried moving itunes to a new computer which proved almost impossible. So I moved my whole library to Google Play...

    I can play my now "google play" library through my apple TV without using itunes, by using my Mac Air and airplay mirroring my screen and sound.

    My question there a loss in sound quality by doing this? I know my library is streaming to my computer at 256...and apple TV to Amplifier is lossless...but is the bridge between my mac air and the apple tv lossless too?

    If it is...that's pretty cool. I'd be streaming my google play music library through apple TV....and does that mean I can stream Spotify in the same way? With no loss of quality as if Spotify was hardwired into the Apple TV too?It soiunds pretty good...but need to know there is no loss...many thanks.

    Many thanks
  9. spacepower7 macrumors 68000

    May 6, 2004
    My understanding is that everything sent from iTunes to the Aiport Express and AppleTV has always been converted to an Apple Lossless stream. I would assume (not sure) that the same would be applied to any audio on Mac OSX sent via the Airplay. I can't see they spending time rewriting the software for a new protocol. Since iTunes will convert an MP3 on the fly to Apple Lossless to send over AirPlay, I would assume it would do the same for any audion on the Mac that can be played via core audio.

    Then again, never assume anything ;)
  10. jonpratt macrumors newbie

    Dec 6, 2012
    Sampling Rates and DAC

    An important factor in determining audio quality from the PTV optical out is the sampling rate. Itunes outputs at a 44 sample rate while the ATV outputs at 48.

    I found this caused audible artefacts that sounded like overload distortion especially on congested./complex passages of music.

    The output fed a mini DAC via toslink and then by phono to stereo amp. The DAC combination was fine through Airport Express. Swapping to another DAC that accepted a 48 sampled input solved all problems and sound is very very good.

    Check the capacity of your DAC/amp to accept 48 sampled input.

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